chapter 22-the pre cam brian earth

8/2/2019 Chapter 22-The Pre Cam Brian Earth

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Chapter

22The PrecambrianEarth


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Geologic Time Scale


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Precambrian History

22.1 Early Earth (p. 620)

90% of Earths history

Evidence that Earth is more than 4.4 billionyears old

Crustal rocks are about 4 billion years old

Meteorites (small fragments of orbiting bodies

that have fallen on Earths surface) have been

dated between 4.5 and 4.7 years old.-scientists feel the parts of the solarsystem were formed at the same time

Moon rock samples dated at 4.45 billion years


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Remnants of Precambrian Rocks


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Formation of Earth (p. 621)

Gravitational Contraction

Gradual accumulation of rock caused anincrease in size and mass.

As mass increases, gravity increases.

Gravity caused the Earths center to squeeze

together.


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22.2: Formation of the Crust

and Continents (p. 623) Differentiation: Denser materials sunk tocenter of Earth (core) and less densematerials stayed at the surface (crust),

resulting in the layers of Earth.

Early crust was constantly recycled

Eventually water entered the mantle andthe first continental crust was formedcalled microcontinents


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22.2 Crust Formation, cont.

Craton: oldest and most stable part of acontinent

Today, most are buried.

Due to erosion, cratons have been exposed insome areas called the Precambrian Shield.

In North America, we call it the Canadian Shield

because most of it is exposed in Canada. Alsoseen in MN, WI, and MI.

Contains valuable nickel, silver, and gold.


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Growth of Continents (p. 625)

Microcontinents collided and formedmassive mountains.

Laurentia was the largest land mass in thePrecambrian period.

when it collided with Amazonia, the firstsupercontinent (like Pangaea) was formed


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Atmosphere formation: Precambrian

22.3 Formation of the Atmosphere and

Oceans (p. 628)

Same time as Earths formation Asteroids, meteors, and other objects that

collided with Earth had water in them. This water vaporized upon collision, forming a

haze around Earth Once Earth was formed, the atmosphere chaned

due to outgassing caused by volcanic eruptions. Later, primary plants evolved that used

photosynthesis and released oxygen. Oxygen began to accumulate in the atmosphere

about 2.5 billion years ago.


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22.3 Stromatolites

Precambrian Fossils The most common Precambrian fossils are

stromatolites. Stromatolites are distinctively layered mounds

or columns of calcium carbonate. They are notthe remains of actual organisms but are the

material deposited by algae. Many of these ancient fossils are preserved in

cherta hard dense chemical sedimentary rock.


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22.3: Evidence of Atmospheres

Formation Rocks: oxidized iron in Archean rocksshow that there was oxygen in theatmosphere at that time

Cyanobacteria (oxygen producers)at thebeginning of the Proterozoic era producedenough oxygen to create locally high

concentrations of iron oxides calledbanded-iron formations.


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22.3: Importance of Oxygen

Animals use oxygen for respiration

Protection from ultraviolet radiation (ozonelayer-3 oxygens bonded together)


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22.3: Formation of the oceans

Scientists think oceans reached theircurrent size very early in Earths history

Water probably originated from volcanicoutgassing and asteroids, comets, andother objects that struck Earth whichbrought water vapor to Earth

As Earth cooled, the water vapor cooled toform water


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Early Paleozoic

22.4 Paleozoic Era: Life Explodes

Following the long Precambrian, the mostrecent 540 million years of Earths history

are divided into three eras: Paleozoic,Mesozoic, and Cenozoic.


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22.4: Origin of Life

Cyanobacteria existed on earth 3.5 b.y.a.

Biologists suggest that the atmospherewas rich with hydrogen, methane, andammonia, which, with the energy oflightning, gave rise to an organicprimordial soup (earliest life)

Organic molecules like amino acidsformed


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22.4: Proterozoic Life

Prokaryotes: unicellular organisms with noorganelles, dominated until the end of thePrecambrian

Eukaryotes: first unicellular, thenmulticellular, with organelles, evolved fromprokaryotes


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Early Paleozoic

Paleozoic Era: Life Explodes

Early Paleozoic History During the Cambrian, Ordovician, and Silurian

periods, the vast southern continent ofGondwana encompassed five continents (SouthAmerica, Africa, Australia, Antarctica, and part ofAsia).


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Gondwana and theContinental Landmasses


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Early Paleozoic


Early Paleozoic Life Life in early Paleozoic time was restricted to the

seas.


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Life in the Ordovician Period


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Late Paleozoic


Late Paleozoic History Laurasia is the continental mass that formed the

northern portion of Pangaea, consisting ofpresent-day North America and Eurasia.

By the end of the Paleozoic, all the continents

had fused into the supercontinent of Pangaea.


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Late Paleozoic Plate Movements


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Late Paleozoic


Late Paleozoic Life Some 400 million years ago, plants that had

adapted to survive at the waters edge beganto move inland, becoming land plants.

The amphibians rapidly diversified because

they had minimal competition from other land

dwellers.


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Armor-Plated Fish

M d l f P l i


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Model of a PennsylvanianCoal Swamp


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The Great Paleozoic Extinction


The worlds climate became very seasonal,probably causing the dramatic extinction of

many species.The late Paleozoic extinction was thegreatest of at least five mass extinctions tooccur over the past 500 million years.


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Mesozoic Era

13.3 Mesozoic Era: Age of Reptiles

Dinosaurs were land-dwelling reptiles thatthrived during the Mesozoic era.

Mesozoic History A major event of the Mesozoic era was the breakup

of Pangaea.


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Mesozoic EraMesozoic Life


Gymnosperms are seed-bearing plants that do

not depend on free-standing water forfertilization.

The gymnosperms quickly became the dominant

plants of the Mesozoic era.

C di R ki W F d


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Canadian Rockies Were FormedThroughout the Cretaceous Period


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Mesozoic EraThe Shelled Egg


Unlike amphibians, reptiles have shell-covered

eggs that can be laid on the land. The elimination of a water-dwelling stage (like

the tadpole stage in frogs) was an importantevolutionary step.


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Mesozoic EraReptiles Dominate


With the perfection of the shelled egg, reptiles

quickly became the dominant land animals. At the end of the Mesozoic era, many reptile

groups became extinct.


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The Flying Reptile Pteranodon


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Fossil Skull of an Extinct Crocodile


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Cenozoic North AmericaThe Cenozoic era is divided into two

periods of very unequal duration, the

Tertiary period and the Quaternary period.

13.4 Cenozoic Era: Age of Mammals

Plate interactions during the Cenozoic eracaused many events of mountain building,volcanism, and earthquakes in the West.


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Cenozoic LifeMammalsanimals that bear live young

and maintain a steady body temperature

replaced reptiles as the dominant landanimals in the Cenozoic era.


Angiospermsflowering plants withcovered seedsreplaced gymnosperms asthe dominant land plants.


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Cenozoic LifeMammals Replace Reptiles


Adaptations like being warm blooded,

developing insulating body hair, and havingmore efficient heart and lungs allow mammalsto lead more active lives than reptiles.


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Fossils from La Brea Tar Pits


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Cenozoic LifeLarge Mammals and Extinction


In North America, the mastodon and mammoth,

both huge relatives of the elephant, becameextinct. In addition, saber-toothed cats, giantbeavers, large ground sloths, horses, camels,giant bison, and others died out on the North

American continent. The reason for this recent wave of extinctions

puzzles scientists.

chapter 22-the pre cam brian earth

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